1. Technical Field
Methods and systems are disclosed herein with respect to adaptive medium access control (AMAC) and, more particularly, AMAC in wireless ad hoc networks, including wireless mobile ad-hoc networks.
2. Related Art
A wireless ad hoc network is a decentralized type of wireless network that does not rely on a preexisting infrastructure, such as routers in wired networks or access points in managed-infrastructure wireless networks. Instead, each node participates in routing by forwarding data for other nodes. A determination as to which nodes forward data is made dynamically based on network connectivity. The decentralized nature of wireless ad hoc networks makes them suitable for a variety of applications where central nodes cannot be relied on.
Wireless ad hoc networks may be classified by their application, such as mobile ad hoc networks (MANET), wireless mesh networks (WMN), and wireless sensor networks (WSN)
Wireless links between nodes may be influenced by node resources, such as transmit power, computing power, and memory. Wireless links may also be influenced by factors such as reliability, link distance, signal loss, interference, and noise.
Since links can be connected or disconnected at any time, an ad-hoc network must be able to provide dynamic restructuring that is timely, efficient, reliable, robust and scalable. In a MANET, where nodes are mobile, dynamic restructuring can be even more challenging.
Due to the extensive variety of possible situations that may occur in wireless ad hoc networks, modeling and simulation may be employed with extensive parameter sweeping and what-if analyses, which may be performed with modeling and simulation tools, such as an open source Network Simulator II (NS2).
In an ad-hoc network, contention amongst nodes for access to a shared wireless medium often results collisions and channel congestion.
Conventional computing/communication networks manage network resources and network access from a dedicated or central control node, and with protocols and infrastructure that are not readily amenable to wireless ad-hoc networks, and particularly not amendable to wireless mobile ad-hoc networks (MANETs).
Conventional wireless local area networks (WLANs) use carrier sense multiple access/collision avoidance (CSMA/CA) technology, such as specified in IEEE standard 802.11. The collision avoidance mechanism employed by CSMA/CA utilizes a random back-off period prior to each transmission. The random nature of the back-off period reduces but does not eliminate the probability of collisions. In order to detect and recover from collisions, an acknowledgment mechanism must be used with each transmitted message. When an acknowledgment is not received, a message may be re-transmitted. With each re-transmit attempt, the back-off period is randomly selected from an expanded contention time window using a binary exponential back-off scheme.
Many published studies have shown that these random back-off and collision recovery schemes significantly compromise the performance of CSMA/CAWLANs in terms of access delay, delay jitter, and network throughput, particularly as the number of stations and offered load increases.
There is a need to for more flexible and adaptive techniques to avoid collisions and congestion.